"Circular marine feed ingredients for Nordic aquaculture"

Niklas Warwas defended his thesis "Novel Marine Ingredients for Aquaculture - Fish Nutrition, Physiology and Intestinal Health" on November 10, 2023.

Niklas Warwa's PhD project aims to find - and more importantly test - sustainable marine protein sources and additives that can replace current ingredients for salmonids. In order to increase fish farming in the world and Sweden, we need to find new feed varieties and Niklas Warwa's search has included yeasts, flies and mackerel in tomato sauce.

Today's fish feed is about 70 % plant-based, with the rest consisting of fish meal and fish oil. In Niklas Warwa's experiment, the alternative feeds have been used to replace less sustainable ingredients. This is to see if they can replace the part of the feed with the highest proportion of essential fatty acids and amino acids. Among the alternatives tested were feeds made from marine yeast and marine insects, something he is not aware of having been done elsewhere.

Protein feed on marine yeast helped fish grow

holding a glass container of fish feed
Niklas Warwas Photo: Xintian Xie

Marine yeast is not sensitive to salt and also has probiotic properties. In the project, fish have been fed with yeast-based protein grown on herring spawn, a residual product from the canning industry in Kungshamn, where he has worked with the Blue Food batch of Smögen salmon. The yeast strain used in the experiments was isolated at Tjärnö Marine Laboratory. For the experiments, it was grown in a so-called bioreactor at Chalmers, a steel container where parameters such as temperature, pH and oxygen can be controlled. During the nine weeks of the experiment, the fish doubled in weight and a lot of time was spent feeding the fish and making sure they were doing well.

To determine whether the fish could digest the yeast and utilize the nutrients, the fish's feces were collected, weighed and analyzed. A large number of parameters were examined, including fish growth, gut health, physiology, and electrophysiology. Many new ingredients are not beneficial for fish, or healthy for fish guts. For example, they can cause inflammation or intestinal diseases. For example, microbial ingredients and insects contain the substance chitin and plants often contain so-called antinutrients. This is one reason why the use of soy flour has decreased in favor of soy concentrate. Salmonids are generally poor at breaking down the sugars found in the cell walls of yeast and insect shells (chitin) and in plants such as cellulose.

The yeast experiments were successful and the fish could utilize over 80% of the feed, which is very high for yeast and bacteria. When the cell walls were first broken down by heat treatment at high air temperature, the availability increased slightly further.

Fly larvae with a taste of the sea

In the project, Niklas Warwas has also bred flies on sugar kelp residues from the Blue Food partner Nordic Seafarm. This is a special type of fly that lays its eggs on seaweed and whose larvae feed on the bacteria that break down the seaweed. It took six months of fly breeding before he had enough larvae for a feeding trial, around 10 kg. But although the work was time-consuming, the results were promising. The nutritional content was closer to fish meal than to other insects used to produce feed. Moreover, the fish seemed to appreciate the taste and ate more.

Fish feed containing insects and yeast is already available but is much more common among fish other than salmonids. A major advantage is that both yeast and insects can be produced from residual products that contribute to circularity. Residues can otherwise be expensive to dispose of, such as herring spawn, which is high in nitrogen. Another advantage is that marine yeast and insects contain valuable omega-3. The need for omega-3 is otherwise the main obstacle to reducing the amount of fishmeal and fish oil in the feed.

So there is an attractive concept here and Niklas Warwas is keen to show the industry that it works. But he leaves the commercial aspects to them.

Additional candidates with varying degrees of success

Other experiments in the project involved the macroalgae Ulva and different types of residual raw materials such as fish guts, pickled herring that failed quality tests, and mackerel in tomato sauce that had passed its expiry date. The fish were fed diets containing 50% of each residual raw material - which is high. Unfortunately, they did not like the pickled herring, which has a low pH and is salty. The mackerel in tomato sauce was also not very popular, but the sprat was liked. Niklas Warwas is planning a follow-up of that part.

Niklas Warwas has a great interest in food production and aquaculture because it is highly topical to use the sea to a greater extent to produce food. The work in the project involves a good mix of hands-on work, writing and also collaboration, which Niklas appreciates.

Niklas Warwas sees great potential for collaboration with Pontus Gunnarsson, whose projects are similar but where Pontus Gunnarsson has a greater interest in taste and the culinary qualities of the end product. He is already collaborating with Marica Andersson in a project that produced protein from Ulva algae. Another of Blå Mat's PhD students whose project is interesting is John Axelsson, who works a lot with side streams from fishing.

The project is particularly relevant to the research areas 1. primary production, 3. circular systems and 6. Health and welfare.

Niklas Warwa's project is expected to be completed in October 2023.

Principal supervisor

Kristina Snuttan Sundell, University of Gothenburg

Assistant supervisor

Elisabeth Jönsson Bergman, University of Gothenburg
Markus Langeland, RISE

Niklas Warwa's profile page on the University of Gothenburg website.